Vapor pressure is the pressure exerted by a vapor when it is in dynamic equilibrium with its liquid (or solid) phase at a given temperature.
How it works:
- In a closed container, some liquid molecules escape into the vapor phase.
- As more molecules evaporate, some begin to condense back into the liquid.
- When the rate of evaporation equals the rate of condensation, the system reaches equilibrium—the pressure at this point is the vapor pressure.
Key points:
- Higher temperature → higher vapor pressure (more molecules have enough energy to escape).
- Substances with high vapor pressure at room temperature (like acetone or ethanol) are considered volatile.
- When vapor pressure equals atmospheric pressure, the liquid boils.
Vapor pressure is crucial in understanding boiling, evaporation, and condensation processes, and plays a key role in meteorology, chemistry, and engineering.